1. Yield gap survey
Kazuki Saito

2. Contents
• What is yield gap?
• Why is yield gap study important?
• Review for previous studies in Africa
• Tentative protocol
• Conclusions

3. What is yield gap?
YGM, model-based yield gap (potential yield is simulated with a model)
YGE, experiment-based yield gap (potential yield is estimated with a field experiment)
YGF, farmer-based yield gap (potential yield is estimated with maximum of farmers’ yields)
(Lobell et al., 2009)

4. Why is yield gap study important?
• Identify areas with potential to increase food supply
• Identify causes of yield gap
• Provide research prioritization
• Identify measures to increase crop production

5. The causes of yield gaps (FAO, 2004)
• Biophysical
• Technical management
• Socio-economic: farmers’ knowledge, household
income/expenses/investment
• Institutional/policy: government policy, rice price, credit, input
supply, land tenure, market
• Technology transfer and linkages: competence and facilities of
extension staff; farmers’ resistance to new technology

6. Previous studies on yield gaps in Africa
• 4 agroecological zones in West Africa
• Irrigated lowland, rainfed lowland and rainfed upland
• Assessment of on-farm yield variation and its causes

7. Assessment of on-farm yield variation
• Crop cut
• Visual estimate
&
• Managements
• Stresses
Iron toxicity effect on rice yield
> 4000 plots surveyed in Ivory
coast, Guinea, Ghana (Cherif et
al., 2009)

8. Yield gaps in West Africa: 40% of potential yield
12 100% potential yield
80% potential yield
On-farm yield (t/ha)
8
4
y = 0.4337x
0
0 4 8 12
Potential yield (t/ha)
Model-based yield gap was used for irrigated lowland, whereas experiment-based yield gap or farmer-
based yield gap was used for rainfed systems.

9. Irrigated lowland in Sahel, Sudan savanna, and Guinea savanna
(Wopereis et al. 1999)
• Timing and amount of N fertilizer
• P and K deficiency
• Unreliable irrigation
• Delayed planting in the wet season
• Weed control
• Late harvesting
Irrigated lowland in Equatorial forest (Becker and Johnson, 1999)
• Water control
• Seedling age
• Time of weeding
• Number of N splits
• P application

10. Rainfed lowland rice (Becker and Johnson, 2001)
• Bunding
• N rate
• Fertilizer N split
• P fertilizer
• Timing of weed control
Rainfed upland rice (Becker and Johnson, 2001)
• Fallow length
• N availability
• Weed management
• Unidentified constraints may be drought, P, soil physical properties, or pests

11. Limitations in previous studies in Africa
• West Africa only
>>> More than 10 countries including East Africa
• Unexplained yield gaps; unidentified factors
>>> field monitoring using simple score (weed
incidence, pest damage, field water condition, salinity and
etc.)
>>> soil nutrients & physical properties

12. Tentative protocol
• Survey plan
• Field survey and data collection
• Follow-up interview (after harvest)

13. Survey plan 1
• Selection of target community and fields by socio-
economic unit, based on diagnostic survey
• 50-100 fields per hub
• Farmers often have several parcels in the community for
rice cultivation, and one parcel is to be selected for this
survey
• Weather station

14. Survey plan 2
• In the first visit, area to be surveyed is determined
(at least 200 m2)
• Field survey is to be made at least every 15-20
days from around 10 days after transplanting or
direct seeding until harvest
• Field observers should not give advice on crop
management practices to farmers

15. Field survey and data collection 1
Data collection at first visit Data collection at 2nd visit to visit before harvest
Code number for each surveyed area & sketching map
Latitude/longitude, and elevation (m)
Rice ecology
Approximate area of the parcel (include surveyed area)
Previous crops or length of fallow
Variety
Irrigation / drainage system
Land preparation method
Crop establishment method and intercropping
Crop density
Soil sampling
Establishment of plots where rice is harvested
Growth stages of rice plants Growth stages of rice plants
Rice canopy cover Rice canopy cover
Water status Water status
Iron toxicity (irrigated or rainfed lowland) Iron toxicity (irrigated or rainfed lowland only)
Alkali Injury & salt injury (irrigated or rainfed lowland) Alkali injury & salt injury (irrigated or rainfed lowland only)
Weed infestation Weed infestation
Canopy cover of crops intercropped with rice Canopy cover of crops intercropped with rice
Diseases
Insect pests

16. Field survey and data collection 2
Data collection on crop management practices (‘rate-and-
date’), through interview and providing sheets in which
farmers can fulfill their activities in the surveyed plot.
• Soil fertility management
• Weed management
• Pesticide use
• Water management

17. Field survey and data collection 3
Data collection at harvest
Rice canopy cover
Water status
Iron toxicity (irrigated or rainfed lowland)
Alkali Injury & salt injury (irrigated or rainfed lowland)
Weed infestation
Canopy cover of crops intercropped with rice
Harvest date
Yield
Lodging incidence
Rice samples for nutrient analysis
Spikelet fertility
Rat/bird damage

18. Follow-up survey
• Constraints and farmers’ poor crop management
practices are identified
Follow-up interview
• Identify causes of poor crop management practices
• Get an idea about a level of farmers’ knowledge of rice
cultivation and technologies use

19. Conclusions
• Multidisciplinary approach
• Intensive field observation + interview
• Training